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1

Digitale Medien

Observation of room temperature surface-emitting stimulated emission from GaN:Ge by optical pumping (1996)

Zhang, X. ; Kung, P. ; Saxler, A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 80 (1996), S. 6544-6546

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Optically pumped surface-emitting stimulated emission at room temperature was observed from GaN:Ge grown by metalorganic chemical vapor deposition. The sample was optically pumped perpendicularly on the top surface while the stimulated emission was collected from the back colinearly with the pump beam. The cavity was formed by the GaN/air and GaN/sapphire interfaces without any other structure. The stimulated emission was gain guided by the pump beam. The threshold optical pump density for stimulated emission was approximately 2.8 MW/cm2 and the linewidth was 2.5 nm. The emission from GaN:Ge showed a redshift as the pump density increased. The comparison between theoretical calculations and experimental results suggested that many-body interactions can account well for the redshift. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.363674

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2

Digitale Medien

Thermal stability of GaN thin films grown on (0001) Al2O3, (011¯2) Al2O3 and (0001)Si 6H-SiC substrates (1994)

Sun, C. J. ; Kung, P. ; Saxler, A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 236-241

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Single crystals of GaN were grown on (0001), (011¯2) Al2O3 and (0001)Si 6H-SiC substrates using an atmospheric pressure metalorganic chemical-vapor-deposition reactor. The relationship has been studied between the thermal stability of the GaN films and the substrate's surface polarity. It appeared that the N-terminated (0001) GaN surface grown on (0001)Si 6H-SiC has the most stable surface, followed by the nonpolar (112¯0) GaN surface grown on (011¯2) Al2O3, while the Ga-terminated (0001) GaN surface grown on (0001) Al2O3 has the least stable surface. This is explained with the difference in the atomic configuration of each of these surfaces which induces a difference in their thermal decomposition.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.357133

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3

Digitale Medien

Crystallography of epitaxial growth of wurtzite-type thin films on sapphire substrates (1994)

Kung, P. ; Sun, C. J. ; Saxler, A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 75 (1994), S. 4515-4519

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: In this article, we present a crystallographic model to describe the epitaxial growth of wurtzite-type thin films such as gallium nitride (GaN) on different orientations of sapphire (Al2O3) substrates. Through this model, we demonstrate the thin films grown on (00⋅1)Al2O3 have a better epilayer-substrate interface quality than those grown on (01⋅2)Al2O3. We also show the epilayer grown on (00⋅1)Al2O3 are gallium-terminated, and both (00⋅1) and (01⋅2) surfaces of sapphire crystals are oxygen-terminated.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.355943

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4

Digitale Medien

A crystallographic model of (00⋅1) aluminum nitride epitaxial thin film growth on (00⋅1) sapphire substrate (1994)

Sun, C. J. ; Kung, P. ; Saxler, A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 75 (1994), S. 3964-3967

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: High-quality thin aluminum nitride films were grown on different orientations of sapphire substrates by metalorganic chemical vapor deposition. (00⋅1) AlN thin film grown on (00⋅1) Al2O3 has better crystallinity than (11⋅0) AlN on (01⋅2) sapphire. Full width at half maximum of a rocking curve is 97.2 arcsec, which is the narrowest value to our knowledge. A crystallographic model between AlN thin films and sapphire substrates was proposed to explain the process of crystal growth. "Extended atomic distance mismatch'' which is the mismatch of atomic distance for a longer period was introduced. It is shown that the mismatch is relaxed by edge-type dislocations. Extended atomic distance mismatch was used to interpret the results that (00⋅1) AlN has better crystallinity than (11⋅0) AlN, but (11⋅0) GaN has better crystallinity than (00⋅1) GaN.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.356017

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5

Digitale Medien

Characterization of an AlGaN/GaN two-dimensional electron gas structure (2000)

Saxler, A. ; Debray, P. ; Perrin, R. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 369-374

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: An AlxGa1−xN/GaN two-dimensional electron gas structure with x=0.13 deposited by molecular beam epitaxy on a GaN layer grown by organometallic vapor phase epitaxy on a sapphire substrate was characterized. X-ray diffraction maps of asymmetric reciprocal lattice points confirmed that the thin AlGaN layer was coherently strained to the thick GaN layer. Methods for computing the aluminum mole fraction in the AlGaN layer by x-ray diffraction are discussed. Hall effect measurements gave a sheet electron concentration of 5.1×1012 cm−2 and a mobility of 1.9×104 cm2/V s at 10 K. Mobility spectrum analysis showed single-carrier transport and negligible parallel conduction at low temperatures. The sheet carrier concentrations determined from Shubnikov–de Haas magnetoresistance oscillations were in good agreement with the Hall data. The electron effective mass was determined to be 0.215±0.006 m0 based on the temperature dependence of the amplitude of Shubnikov–de Haas oscillations. The quantum lifetime was about one-fifth of the transport lifetime of 2.3×10−12 s. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.371869

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6

Digitale Medien

Infrared properties of AgGaTe2, a nonlinear optical chalcopyrite semiconductor (1999)

Ohmer, M. C. ; Goldstein, J. T. ; Zelmon, D. E. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 86 (1999), S. 94-99

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The fundamental optical properties of AgGaTe2, a nonlinear optical semiconductor are reported. These properties include birefringence, indices of refraction, infrared transmission, and the temperature dependence of the band gap. The average index for wavelengths greater than several microns was found to be 3.0. The birefringence was found to be rather large and to range from a near band edge value of 0.038 at 1.3 μm to a value of 0.017 at 15 μm. Additionally, native defect related sub-bandgap absorption, photoluminescence, and electrical transport have been studied in these nominally undoped p-type crystals. An activation energy associated with these defects was determined to be 0.3 eV and the corresponding photoluminescence and absorption data showed, respectively, a broad asymmetric emission band centered at 0.8 eV and two bands at 0.95 and 1.01 eV, the absorption band at 0.95 eV being the most intense. The measured properties were utilized to assess the potential of AgGaTe2 for the wavelength conversion processes of second-harmonic generation and degenerate optical parametric oscillation. It was found that AgGaTe2 will not phase match at room temperature. However, it is estimated that mixed crystals of the form AgGa(Se(1−x))Tex)2 for a Te addition of 19% can exceed the conversion efficiency of AgGaSe2 by more than 100%. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.370704

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7

Digitale Medien

Persistent photoconductivity study in a high mobility AlGaN/GaN heterostructure (2000)

Elhamri, S. ; Saxler, A. ; Mitchel, W. C.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 88 (2000), S. 6583-6588

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We have used the Shubnikov–de Haas and the Hall effects to investigate the effect of subband gap illumination on the transport properties of a very high mobility, μ=54 000 cm2/V s at T=1.2 K, Al0.09GaN0.91/GaN heterostructure. We have found that this illumination resulted in a photocurrent that was persistent at low temperatures. This photocurrent, which led to an increase in the carrier density, was used to study the dependence of the mobility and the quantum scattering time on the carrier density. Unlike in previous studies of persistent photoconductivity in GaN and AlGaN/GaN by other researchers, we have found that the mobility did not always increase with the carrier density as a result of illumination. For small duration of illumination, the mobility increased with the carrier density. However additional illumination resulted in a decrease of the mobility despite the increase in the carrier density. We believe that screening is responsible for the initial increase in the mobility, while ionization of defects in GaN, interface charges, and alloy disorder may be responsible for the eventual decrease in the mobility. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1322386

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Dissociation of Al2O3(0001) substrates and the roles of silicon and oxygen in n-type GaN thin solid films grown by gas-source molecular beam epitaxy (2000)

Van Nostrand, J. E. ; Solomon, J. ; Saxler, A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 8766-8772

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Unintentionally doped and silicon doped GaN films prepared by molecular beam epitaxy using ammonia are investigated. Hall, secondary ion mass spectroscopy (SIMS), photoluminescence, and x-ray data are utilized for analysis of sources of autodoping of GaN epitaxial films in an effort to identify whether the n-type background electron concentration is of impurity origin or native defect origin. We identify and quantify an anomalous relationship between the Si doping concentration and free carrier concentration and mobility using temperature dependent Hall measurements on a series of 2.0-μm-thick GaN(0001) films grown on sapphire with various Si doping concentrations. SIMS is used to identify oxygen as the origin of the excess free carriers in lightly doped and undoped GaN films. Further, the source of the oxygen is positively identified to be dissociation of the sapphire substrate at the nitride-sapphire interface. Dissociation of SiC at the nitride-carbide interface is also observed. Finally, SIMS is again utilized to show how Si doping can be utilized to suppress the diffusion of the oxygen into the GaN layer from the sapphire substrate. The mechanism of suppression is believed to be formation of a Si–O bond and a greatly reduced diffusion coefficient of the subsequent Si–O complex in GaN. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.373608

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9

Digitale Medien

Fermi level control and deep levels in semi-insulating 4H–SiC (1999)

Mitchel, W. C. ; Perrin, R. ; Goldstein, J. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 86 (1999), S. 5040-5044

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Temperature dependent Hall effect, optical admittance spectroscopy, and optical absorption measurements of semi-insulating bulk 4H–SiC are reported. Both intentionally vanadium doped material and commercial grade semi-insulating material were investigated. The carrier concentration versus inverse temperature results from Hall effect measurements up to 1000 K indicated the samples were dominated by one of two deep levels near midgap. In addition to the deep donor level of substitutional vanadium, Ec−1.6 eV, we observed another level at Ec−1.1 eV in some samples, indicating that levels other than the vanadium donor can pin the Fermi level in semi-insulating SiC. Optical admittance measurements on the semi-insulating material indicate the presence of levels at Ec−1.73 and 1.18 eV that were previously observed in conducting samples with this technique and we attribute these levels to the same defects producing the 1.1 and 1.6 eV levels seen by Hall effect. Secondary ion mass spectroscopy measurements of dopant and impurity concentrations are reported. Even though vanadium is present in all of these samples, along with other impurities we are at present unable to definitively identify the 1.1 eV level. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.371476

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10

Digitale Medien

Photovoltaic effects in GaN structures with p-n junctions (1995)

Zhang, X. ; Kung, P. ; Walker, D. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 67 (1995), S. 2028-2030

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Large-area GaN photovoltaic structures with p-n junctions have been fabricated using atmospheric pressure metalorganic chemical vapor deposition. The photovoltaic devices typically exhibit selective spectral characteristics with two narrow peaks of opposite polarity. This can be related to p-n junction connected back-to-back with a Schottky barrier. The shape of the spectral characteristic is dependent on the thickness of the n- and p-type regions. The diffusion length of holes in the n-type GaN region, estimated by theoretical modeling of the spectral response shape, was about 0.1 μm. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.114776

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